Flexible power cable



March 13, 1962 J. w. OLSON FLEXIBLE POWER CABLE Filed April 6, 1959 FIG.3

FIG. 2

INVENTOR John W. Olson Y @4 42; 6N Z 4 ATTORNEYS 3,025,340 Patented Mar.13, 1962 iiic 3,025,340 FLEXIBLE PUWER CABLE John W. @lson, Dobbs Ferry,N.Y., assignor to Anaconda Wire and Cable Company, a corporation ofDelaware Filed Apr. 6, 1959, Ser. No. 804,341 4 Claims. (Ci. 174120)This invention relates to flexible electric power cables of the typeinsulated with Wrappings of paper tape. More particularly, the inventionprovides a paper-insulated flexible power cable which is characterizedin that the paper tape of the insulation is embossed with a plurality ofsubstantially regularly spaced non-rectilinear convexities.

Paper tape is often used as insulation on flexible electric cables andon power cable leads in transformers and the like, because it inherentlyhas good dielectric strength and is inexpensive, easy to apply, and canbe made to withstand the flxing and bending to which such cables andleads are often subjected. Also, a wrapping of paper can easily absorb aliquid dielectric if such is used, as in transformer leads which aresubmerged in oil in the transformer housing. To increase the flexibilityof such paper-insulated electric cables, it has been proposed heretoforeto form the paper wrappings from randomly crumpled paper or crepe papertapes, rather than from tapes of ordinary flat paper, because the formerare extensible and can stretch when the cable is flexed.

However, tapes of randomly crumpled or crepe paper have not provedentirely satisfactory for use as insulation on power cables. One of theprime disadvantages of both types of paper is that during theirmanufacture the individual fibers are deformed to such an extent thatmany are torn apart. For example, crepe paper is pre pared by crowding asheet of thin wetted paper on a roll so that the paper is folded into amultitude of acute pleats, and during the process fibers along thefold-lines of the pleats are severely damaged. Such damage to the fibersof a paper tape increases the susceptibility of insulating wrappingsmade from them to electrical and mechanical deterioration.

A further disadvantage of randomly crumpled and crepe papers is thatsuch papers are necessarily of light weight and low density. As aresult, they are less suitable for purposes of elctrical insulation thanharder and denser papers because the insulating ability of papergenerally increases with its density. Also, crepe paper be comespermanently deformed when stretched perpendicular to its pleats. Hence,when a cable wrapped with such paper is bent and then bent back to itsoriginal form, the Wrapping is permanently distorted and loosened.

It is the purpose of the present invention to provide a paper-insulatedelectric cable which does not suffer from any of these disadvantages andyet is exceptionally flexible. Broadly stated, the invention provides aflexible power cable comprising an electrical conductor, and a pluralityof layers of paper tape wrapped about the con ductor. Rather than beingflat, crumpled, or creped, the paper of the tape in this new cable isembossed with a plurality of substantially regularly spaced convexitiesdefined by a plurality of surfaces joined at rounded junctions withoutsharply folding the paper of the tape.

Paper of this type possesses many advantages over randomly crumpled orcrepe papers. Not only is it substantitially free from broken fibers asdescribed above, but it is extensible both laterally and longitudinally.In the embossing of the paper used in the power cable of the invention,the convexities impressed in the paper are shaped without forming sharp,acute fold-lines. Thus, the individual fibers of the paper are notseverely bent and are intact throughout the embossed tape. Moreover,

the paper tape of the present cable can be stretched resiiiently in anydirection without permanently deforming. Also, because the convexitiesof this tape are embossed in the paper, rather than being formed bywrinkling or crowding the paper on a roll, a much harder and denserpaper can be employed.

Even when wrapped under tension, embossed paper of this type does notflatten out, so that each turn of the wrapped tape contacts only theraised surface of the previous turn. Hence, the tape forms a cushioninginsulating layer about the conductor which yields easily to the internalradial forces imposed on it when the cable is bent, thereby improvingthe flexibility of the finished wrapping.

A preferred embodiment of the flexible power cable of the invention isdescribed hereinbelow with reference to the accompanying drawing,wherein FIG. 1 is a perspective showing a length of the new power cable;

FIG. 2 is a plan of a portion of one form of the embossed paper tapewhich may be used in the power cable of the invention; and

E6. 3 is a cross section on an enlarged scale taken along the line 33 ofFIG. 2.

Referring first to FIG. 1, a length of flexible cable 10 is shownprovided with a stranded copper conductor 11. Wrapped helically aboutthe conductor 11 are a plurality of turns of a paper tape 12 formingconcentric layers of insulation 14. To protect the outermost turns ofthe tape, an outer braided jacket 16, preferably of cotton, is appliedthereon.

Advantageously, the tape 12 is formed from a relatively hard calenderedkraft paper because the higher density of such paper increases thedielectric properties of the wrapping, and its hardness facilitatesretaining an embossed pattern. The paper can vary in thickness so longas its possesses suflicient strength to be helically wrapped undertension in the conventional manner about the conductor 11 and issufiiciently flexible for its particular application. If the surface ofthe paper possesses a smooth calendered finish the cable 10 is moreflexible because the friction between layers in the wrapping 14 is thenreduced and the adjoining layers of the tape 12 can slide more easilyover one another when the cable is flexed.

According to the invention, the paper of the tape 12 is embossed with aplurality of regularly arranged spaced convexities, one form of which isshown in detail in FIGS. 2 and 3. Thus, a plurality of zigzagging ridges18 are embossed parallel to one another along the length of the tape.The ridges 18 are spaced apart regularly on the surface of the tape sothat a corresponding plurality of grooves 20 are defined therebetween.

The plateaus of the ridges 18 and the valleys of the grooves 20 aredefined by substantially planar surfaces and are joined together byobtusely sloping surfaces 21 so that the included angles therebetweenare always greater than and with the junction 22 between the slopingsurfaces and the valleys rounded instead of being sharply folded. As aresult, the fibers of the paper are not subjected to severe bending orcreasing during the embossing of the ridges and grooves and aregenerally left intact throughout the paper after completion of theembossing operation. These ridges and grooves 18 and 20 may be formed bypassing a calendered kraft paper through opposed rotating heated rollerdies having mating zigzagging lands and grooves on their cylindricalsurfaces which impress the paper into its embossed form.

The plateaus of the ridges 18 may be raised only between about 0.003 and0.020 inch above the Valleys of the grooves 20 though they may behigher. Such low height of the ridges 18 further insures that the fibersof the paper are not torn or damaged during the embossing operation; yeteven with such low height the zigzagging ridges 13 are sufficiently highto impart substantial extensibility, both lateral and longitudinal, tothe tape and to provide a marked cushioning effect to the plurality oflayers of tape superimposed upon one another in the wrapping.

When a tape 12 of the type shown in FIGS. 2 and 3 is wrapped about theconductor 11, the layer of insulation 14 which builds up is relativelyspongy because of the embossed construction of the tape. Even under thetension imposed in helical wrapping operations, the ridges 18 do notcompletely flatten out. As a result, the internal radial compressiveforces imposed on the tape when the cable is bent are readily absorbed,so that flexing of the cable is easy, and the wrapping is prevented frombinding itself into an inflexible layer about the conductor. Also, thecushioning construction permits each turn of the finished wrapping toslide relative to the adjoining turns when the cable is bent so that thelayers can easily re-orient to conform with the curve of the bend. Inaddition, a certain amount of both longitudinal and lateral resilientstretching of the tape 12. is permitted, as a result of the zigzaggingform of the embossed ridges 118.

There are, of course, many other patterns of substantially regularlyspaced convexities which may be embossed on the paper tape, such aspatterns of raised triangles or hexagons, or of alternate octagons andsquares, or of ridges and grooves which follow a course conforming to asuccession of alternately inverted half-hexagons, rather than thezigzagging form shown, to give it the desired properties. In general,the important requirements of any pattern contemplated are that itshould not involve any acute creasing of the paper which might causeinjury to the fibers and also it should provide for resilientextensibility of the tape both longitudinally and laterally.

I claim:

1. A flexible power cable comprising an electrical conductor, and aplurality of layers of dense smooth-surfaced, embossed paper tapewrapped about said conductor, substantially the entire area of saidembossed paper being formed with contiguous alternate concavities andconvexities, said concavities and convexities merging directly into oneanother along rounded junctions without sharply folding the paper ofsaid tape, said concavities and convexities being disposed in anon-rectilinear arrangement defining a pattern free of any straight linepath lying in the paper and extending in a flat plane in any directionacross the paper, said paper being in consequence of said arrangement ofconvexities and concavities extensible simultaneously in more than onedirection without elongation of the paper itself.

2. A flexible power cable comprising an electrical conductor, and aplurality of layers of dense, smooth-surfaced, embossed paper tapewrapped about said conductor, substantially the entire area of saidembossed paper being formed with contiguous alternate concavities andconvexities merging directly into one another along obtusely adjoiningsurfaces, said concavities and convexities being disposed in anon-rectilinear arrangement defining a pattern free of any straight linepath lying in the paper and extending in a fiat plane in any directionacross the paper, said paper being in consequence of said arrangement ofconvexities and concavities extensible simultaneously in more than onedirection without elongation of the paper itself.

3. A flexible power cable comprising an electrical conductor, and aplurality of layers of dense, smooth-surfaced, embossed paper tapewrapped under tension about said conductor, substantially the entirearea of said embossed paper being formed with contiguous alternateridges and grooves extending in a zig-zag path across the paper, saidridges and grooves merging directly into one another along obtuselyadjoining surfaces, said ridges and grooves forming a non-rectilinearpattern free of any straight line path lying in the paper and extendingin a fiat plane in any direction across the paper, said paper being inconsequence of said arrangement of ridges and grooves extensiblesimultaneously in more than one direction without elongation of thepaper itself.

4. A flexible power cable comprising an electrical conductor, aplurality of layers of dense, smooth-surfaced embossed paper tapehclically Wrapped under tension about said conductor, and an outerprotective braided jacket covering said layers of paper tape,substantially the entire area of said embossed paper being formed withcontiguous zigzagging alternate ridges and grooves, said ridges andgrooves merging directly into one another along obtusely adjoiningsubstantially planar surfaces, said surfaces being joined at roundedjunctions without sharply folding the paper of said tape, saidzigzagging ridges and grooves defining a non-rectilinear pattern overthe entire surface of said tape which is free of any straight line pathlying in the paper and extending in a flat plane in any direction acrossthe paper, said paper being in consequence of said pattern of ridges andgrooves extensible simultaneously in more than one direction withoutelongation of the paper itself.

References Cited in the file of this patent UNITED STATES PATENTS463,107 Degenhardt Nov. 10, 1891 1,939,264 Hill Dec. 12, 1933 2,038,935Hunter et al Apr. 28, 1936 2,233,592 Dunajeff Mar. 4, 1941 2,607,822Crandall Aug. 19, 1952 2,607,824 Camilli et a1 Aug. 19, 1952 FOREIGNPATENTS 19,951 Great Britain of 1900 OTHER REFEREI CES Fischer (German),printed App. SN. $30,496, Mar. 29, 1956.

